A New Synthetic Route to Calcium Polyphosphates

Abstract

This study describes the use of flux methods as a novel synthetic route to some known and new calcium polyphosphates, with a view to developing new biomaterials. Calcium acid pyrophosphate, CaH2P2O7, which is a known precursor in the preparation of many other calcium polyphosphates, has been synthesized as a pure crystalline phase in a single step synthesis at temperatures between 190-250 °C. Reaction temperatures between 250 and 400 °C led to the synthesis of γ-Ca(PO3)2, a previously uncharacterised polymorph of calcium metaphosphate. Lattice parameters of a = 10.3682(1) Å, b = 9.5001(1) Å, c = 9.5552(1) Å, with β angle of 93.45(4)° were obtained from powder X-ray diffraction data. A subsequent increase in reaction temperature to 550 °C was found to produce a calcium polyphosphate glass. A detailed study of thermal stability of CaH2P2O7 was also performed to determine phase stability and decomposition pathways.